In a water treatment facility such as a purification plant, a precipitation treatment is carried out by introducing a ground water or surface water as a raw water to a receiving well, and adding a coagulant in a coagulation-sedimentation equipment to form flocs. Then, a settled water is passed through a sand filtration apparatus to remove suspended matters, and finally, conducted a chlorine treatment for disinfect to supply customers. In order to ensure an effect of the chlorine treatment for disinfect more reliably, a intermediate chlorination is performed in which a chlorine is injected to a sedimentation water at a prechlorination for injecting a chlorine prior to a coagulant injection point. The prechlorination is effective in removing an ammonia nitrogen and microorganisms, or oxidized-removing an iron and manganese in the raw water. With respect to a raw water having a high trihalomethane formation potential, it is preferable to adopt a intermediate chlorination for a reduction of trihalomethane.
A change-over of the individual chlorine treatments is not automatically controlled, but is operated by an operator based on his or her feeling and experience, watching the raw water quality.
When the raw water cannot be treated with the usual treatment because of a deterioration of the raw water quality, a powdered activated carbon is thrown into the receiving well or the like so that dissolved matters are absorbed in the activated carbon. The dissolved matters are removed at a subsequent coagulation-sedimentation treatment. The thrown amount of the activated carbon is neither automatically controlled, but is operated by an operator based on his or her feeling and experience, watching the raw water quality to decide the thrown amount.
In a water treatment field, specifically a water purification treatment, a chlorine treatment is prevalently used for a disinfect treatment and a removal of iron and manganese, as stated above. In the case where a trihalomethane precursor is mixed in a raw water, a trihalomethane is generated by a chlorine treatment. Since the trihalomethane is a carcinogenic substance, the generation of trihalomethane must be constrained in a water treatment process.
Currently, it is impossible to monitor in an online mode measurement of trihalomethane and trihalomethane precursor, as it takes long time and costs money. An ozone treatment and an activated carbon treatment are effective ones for removing the trihalomethane precursor. However, there are few treatment plants having an ozone treatment.